234 ORDINARY BRONZES 2. Determination of the Antimony.—The filter-paper with the antimony sulphide is heated in a beaker with 4 c.c. of 50% sodium hydroxide solution and 20-30 c.c. of sodium sulphide (D = 1-225) until the antimony sulphide is completely dissolved. After some time the liquid is filtered directly into the Classen dish, the vessel and filter being washed with 50-60 c.c. of sodium sulphide. The filtrate is treated with 5-6 grams of potassium cyanide to decolorise the sodium sulphide and to prevent formation of polysulphides during the electrolysis, which is carried out at the ordinary temperature. Cathode, Classen capsule; anode, disc or spiral; ND100 = 0-15-0-18 arr.p.; voltage = 1-1-2 ; duration (0-1-0-15 gram Sb) = 15-18 hours. When the antimony is all deposited, the anode is withdrawn, the cap- sule rapidly emptied, washed with water, alcohol and ether, and dried at 70°. The antimony is afterwards removed from the dish by treatment with nitric acid (D 1-2) containing a little tartaric acid in solution. 3. Determination of the Copper, Lead, Iron and Zinc.—The liquid from which the metastannic acid was separated (see i) is acidified with 15-20 c.c. of nitric acid (D 1-2), mixed with the nitric acid solution of the oxides extracted from the metastannic acid and the. whole treated as in the analysis of ordinary brass (q.v.). 4. Determination of the Nickel.—See Nickel Bronzes. 5. Determination of the Manganese.—See Manganese Bronzes. 6. Determination of the Silver.—5-10 grams of the sample are treated with nitric acid and freed from metastannic acid in the ordinary way. In the filtrate the silver is precipitated with hydrochloric acid by the procedure followed for the determination of silver in copper.1 7. Determination of the Phosphorus.—See Phosphor Bronzes. 8. Determination of the Arsenic.—See Copper. 9. Determination of the Sulphur. —2 grams of the sample are treated with nitric acid and the stannic acid separated as usual. From the filtrate the copper is eliminated by electrolysis in nitric acid solution, the residual liquid being evaporated to dryness and the sulphur then deter- mined as in copper (q.v.). B. Gravimetric Method 1. Determination of the Tin.—In a covered beaker, 1-2 grams of the alloy as filings are treated with 15-20 c.c. of nitric acid (D 1-3), the metastannic acid being separated, washed, ignited in a porcelain crucible and weighed: Sn02 x 0-7881 = Sn. The filtrate is treated as in 3. The stannic oxide thus weighed is always impure and, where an exact determination is necessary, it is powdered in an agate mortar, mixed with 6 parts of a mixture of ignited sodium carbonate and sulphur in equal pro- portions, and heated at a gentle heat with the crucible covered until all the sulphur is expelled. 1 Since silver is deposited with the copper on the cathode, the data relating to copper must be corrected by the amount found.and ether, and dried at 70°.